The present invention relates generally to fume control in steel making operations and more particularly to fume control in the strand casting of steel to which fume-emitting ingredients are added.
Examples of fume-emitting alloying ingredients are lead and bismuth which are added to molten steel to improve the machinability properties of the solidified steel product.
In the strand casting of steel, molten steel is introduced from a ladle into a tundish from where the molten steel is directed into a casting mold where at least an outer shell of solidified steel is formed.
The fume-emitting ingredients may be added to the molten steel in the ladle, or they may be added to the stream of molten steel flowing from the ladle to the tundish. Aside from the ladle, fumes may be emitted from the molten stream between the ladle and the tundish and from th molten steel in the tundish.
In the strand casting process, the partially solidified steel moves downstream from the casting mold into a spray chamber in which the steel is sprayed with water to cool the steel and further solidify it. The solidified steel then moves into a run-out chamber located at the downstream end of the spray chamber. Relatively clean gases, devoid of fumes from the fume-emitting gases, are generated in the spray chamber and in the run-out chamber.
After the run-out chamber, the solidified steel strand moves to a torch-cutting station located immediately downstream of the run-out chamber where the strand is cut into pieces. Torch-cutting of the strand generates fumes from the fume-emitting ingredients in the solidified steel strand. These fumes must be prevented from escaping into the work place environment surrounding the strand casting equipment because the fumes can pose a health hazard. In the case of lead, the law restricts the quantity of lead bearing material which may be present in the work place environment as dust or fumes to no more than 50 micrograms per cubic meter.
The fumes emitted from the molten steel, or from the strand during the torch-cutting step, are at least initially in the form of lead or bismuth vapors which may then react with the atmosphere to form oxides of lead or bismuth. In accordance with the present invention, it matters not whether the fumes from the fume-emitting ingredients are in the form of metallic vapors or the oxides thereof. Both forms are equally undesirable.
Gases carrying fumes collected from steel making operations are normally passed through a bag house which removes the fumes from the carrying gases which are then exhausted to the atmosphere minus the fumes.
At the torch-cutting station, water sprays are used to wash scale and dross resulting from the torch-cutting step into a flume located beneath the steel strands at the torch-cutting station. Fumes generated during the torch-cutting step are removed from the torch-cutting locale by exhaust ducts. Because of the water sprays employed at the torch-cutting station, the gases exhausted from this location are wet and cool. It is undesirable to process wet, cool gases through a bag house because the moisture in such gases can precipitate in the bag house and interfere with the ability of the bag house to perform its fume-removing function.